I know one can delete all documents from a certain type via deleteByQuery.
Example:
curl -XDELETE \'http://localhost:9200/twitter/tweet/_query\' -d \
The Delete-By-Query plugin has been removed in favor of a new Delete By Query API implementation in core. Read here
curl -XPOST 'localhost:9200/twitter/tweet/_delete_by_query?conflicts=proceed&pretty' -d' { "query": { "match_all": {} } }'